A communication system typically involves transmitting an information signal from a transmitter to a receiver over a communication channel. The communication channel can include a microwave radio link, a satellite channel, a fiber optic cable, or a copper cable to provide some examples. A communication channel contains a propagation medium that the information signal passes through before reception by the receiver.
The propagation medium of the communication channel may introduce distortion into the transmitted information signal causing a received information signal to differ from the transmitted information signal. Transmission over a multiplicity of paths of different and variable lengths, bandwidth limitations, or transmission at a frequency greater than the capability of the communication channel to provide some examples may introduce distortion into the transmitted information signal. This distortion may cause the received symbols within the received information signal to differ in amplitude and temporal duration from the transmitted information signal. The difference in amplitude and duration may lead to intersymbol interference (ISI) between adjacent symbols within the received information signal. The consequent overlap of individual symbols caused by intersymbol interference may reduce the ability of the receiver to reliably distinguish between individual signal elements of the received information signal.
Communication systems may use an adjustable filter in the form of an equalizer to reduce the effect of the distortion caused by the communication channel. Conventional equalizers may compensate for the distortion caused by a linear communication channel. Linear communication channels may be characterized by linear transfer functions relating the symbols of the received information signal to the symbols of the transmitted information signal. Compensation for the distortion caused by the linear communication channel involves implementing the conventional equalizer with a transfer function that is an inverse of the linear transfer function of the communication channel.
However, the propagation medium of the communication channel may also introduce non-linear distortion into the symbols of the received information signal for which the conventional equalizer may not compensate. Techniques to compensate for the non-linear distortion caused by the communication channel have been implemented within the digital domain, but that is not the case for the analog domain, especially for high speed analog applications. Therefore, what is needed an equalizer that is capable of compensating for the non-linear effects resulting from the communication channel in a communication system for high-speed analog applications.
The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.